An alternator is mounted on a vehicle to supply power to an electric load of the vehicle and to charge a storage battery in accordance with an electricity storage condition, using the power output shaft of the engine as a power source. The output of this alternator depends on the rotational speed of a rotor and an electric power demand. Accordingly, electric power is generated when the electric power demand increases even during acceleration of the vehicle, and therefore the driving force from the power output shaft of the engine is required. This further increases the load energy required for acceleration of the vehicle. During deceleration of the vehicle, little electric power is generated under some electric power using conditions, and the kinetic energy of the vehicle is dissipated as brake heating and the like and as pumping loss of the engine.
The electric power demands for a vehicle in recent years has increased due to the addition of electrical equipment such as an anti-braking system (ABS), a four-wheel drive system (4WS), a traction control system (TRC), a power steering system (PS) and the like. In order to supply sufficient electric power to satisfy this increased demand, the capacity of the alternator tends to increase; however, the efficiency of the alternator is around 50% at maximum.
In general, the energy which can be taken out from the power output shaft of the engine is around 30% of the energy contained in fuel in an automotive vehicle having a gasoline-fueled engine. The energy necessary for the normal running of the vehicle is similarly around 25%. In contrast, when the maximum electric power generation is made using the alternator having, an electric power generation capacity of 1 kW, for example, 2 to 3 kW of the energy to be used for running of the vehicle is consumed by the electric power generation of the alternator. This corresponds to about 6 to 9% of the energy contained in gasoline fuel. Accordingly, the fuel economy is degraded 19 to 26% at maximum electric power generation.
In order to improve the electric power supply in such a vehicle, an electric power supply source which is used in addition to the conventional alternator and does not use the power output shaft of the engine as an energy source, or a control manner for the electric power obtained by this are proposed in Japanese Patent Provisional Publication 61-254082, Japanese Patent Provisional Publication No. 63-262075 and Japanese Patent Provisional Publication No. 5-111101. Of these, both the electric power supply sources disclosed in Japanese Patent Provisional Publication No. 61-254082 and Japanese Patent Provisional Publication No. 63-262075 use an exhaust gas heat electric power generation device which converts the thermal energy of exhaust gas discharged from an internal combustion engine to electric energy. This exhaust gas heat electric power generation device includes a heat absorption section in contact with exhaust gas, a cooling section in contact with outside air or liquid, and a thermoelectric converter element interposed between the heat absorption section and the cooling section to convert to electric energy the thermal energy due to a temperature difference.
Additionally, the electric power supply source and the electric power control method disclosed in Japanese Patent Provisional Publication No. 5-111101 is provided with a solar electric power generating means for converting solar energy to electric energy, in addition to thermoelectric converting means for converting exhaust gas thermal energy from the engine to electric energy as mentioned above. During the running and idling of the vehicle, exhaust gas thermal energy from the engine is converted to electric energy to be stored in a storage battery by using the thermoelectric converting means. When the vehicle is located outside, solar energy is converted to electric energy to be stored in the storage battery by using the solar electric energy generating means. The stored energy is utilized as energy for driving auxiliary electrical equipment parts, accessories, and the like.
Applying the above-described exhaust gas heat electric power generation device theoretically contributes to fuel economy improvements. However, since the amount of electric power generation is around 100 W, it is impossible to satisfy the electric power requirements of the vehicle only with the exhaust gas heat electric power generation device.
Additionally, the reduction in fuel consumption is as small as around 5% merely by using, as an energy for driving accessories and the like, the electric power obtained by the electric power supply source other than the alternator, such as the thermoelectric converting means utilizing exhaust gas heat and the solar electric power generating means utilizing sunlight. Thus, the conventional techniques are relatively ineffective in improving fuel economy improvement and therefore are not practical.
In view of the above-described conventional techniques, there is a need for an electric energy supply system for a vehicle, which can reduce fuel consumption in all vehicle driving modes by controlling the amount of generated electric power obtained from a variety of electric power generating sources, in accordance with the driving condition of the vehicle and the electricity storage condition of a storage battery.
This and other needs are met by the present invention, which provides an electric energy supply system for a vehicle, comprising a plurality of electric power generators for generating electric power by utilizing different energies which can be taken out from a driving source for driving the vehicle. Electricity storing devices are provided for storing electric energy. Driving condition judging means judge a driving condition of the vehicle and electricity storage condition judging means judges an electricity storage condition within the electricity storing means. Electric power controlling means for control a supply amount of electric energy to be used in the vehicle. The controlling means is configured to control an amount of electric power generated by each of the plurality of the electric power generating sources in accordance with information obtained from the driving condition judging means and the electricity storage condition judging means.
In certain embodiments of the invention, the driving source includes an internal combustion engine, and the plurality of the electric power generators includes a power output shaft electric power generator for generating electric power by utilizing a power energy obtained from the internal combustion engine, and an exhaust gas electric power generator for generating electric power by utilizing exhaust gas energy of the internal combustion engine.
The exhaust gas electric power generator includes a thermoelectric generator for generating electric power by utilizing a heat energy of exhaust gas discharged from the internal combustion engine, in certain embodiments of the present invention. In further embodiments of the invention, the exhaust gas electric power generator includes a turbine generator for generating electric power by utilizing kinetic energy of exhaust gas discharged from the internal combustion engine.
Additionally, in an electric energy supply system for a vehicle according to certain embodiments of the present invention, the electric power controlling means is configured to operate the exhaust gas electric power generating means as a main generating source to generate electric power and to supply an electric energy obtained by this electric power generation to the electricity storing means and to an electric power load within the vehicle, when the vehicle is in an acceleration condition that is detected by the driving condition judging means.
The present invention, in certain embodiments, has the electric power controlling means configured to operate the power output shaft electric power generating means as a main generating source to generate electric power and to supply an electric energy obtained by this electric power generation to the electricity storing means and to an electric power load within the vehicle, when the driving condition judging means detects that the vehicle is in an acceleration condition.
Certain embodiments of the present invention provide detecting means for detecting an electric power generating ability of the exhaust gas electric power generator, in which the electric power controlling means is configured to operate the power output shaft electric power generator as a main generating source when the electric power generating ability detected by the detecting means is not higher than a predetermined level.
One of the advantages of the present invention is that by controlling the amount of electric power generated by each of the plurality of the electric power generators in accordance with the driving condition of the vehicle and the electricity storage condition of the storage battery, the energy released from the driving source of the vehicle can be recovered without waste so as to be effectively utilized as electric energy. The invention largely reduces energy consumption in the driving source.
Another advantage is that the kinetic energy and the exhaust gas energy obtained from the internal combustion engine is effectively recovered in accordance with the running modes of the vehicle and the electricity storage condition of the electricity storing means so as to be utilized as electric energy. The fuel to be consumed in the internal combustion engine can be reduced, thereby attaining improvements in fuel economy.
Additionally, the thermal energy of exhaust gas discharged from the internal combustion engine can be recovered by the relatively simple construction of certain embodiments of the invention, thereby not only attaining the fuel economy improvement but also making the improvement practical.
According to certain embodiments of the electric energy supply system for a vehicle, since the turbine generator utilizing the kinetic energy of exhaust gas discharged from the internal combustion engine is used, energy to be discharged can be effectively recovered to attain improvements in fuel economy even though exhaust gas is at a relatively low temperature, if the engine speed is high and the speed of exhaust gas is high. This is especially advantageous under a running mode in which the temperature of exhaust gas is low at a time immediately after engine starting.
In certain embodiments the present invention, when the vehicle is in an acceleration condition, the discharged energy from the engine is recovered and converted into electric energy by the exhaust gas electric power generator. This converted electric energy is supplied to the electricity storing means, or otherwise satisfies the electric load in the vehicle. In other words, since the energy amount contained in exhaust gas is large during acceleration of the vehicle, the electric power to be required for the vehicle can be sufficiently satisfied by electric power generation just by the exhaust gas electric power generation. It is therefore unnecessary to generate electric power through operation of the power output shaft electric power generator which requires the shaft output of the internal combustion engine. By the synergistic effect provided in the present invention, the fuel to be consumed is reduced thereby offering improvements in fuel economy. Particularly, the energy used by the conventional alternator is about 6 to 9% of the energy amount contained in fuel. With the present invention, a fuel economy improvement of 19 to 26% at maximum is attained, in a condition where the alternator is not operated.
According to the electric energy supply system for a vehicle, according to certain embodiments, when the vehicle is in a deceleration condition, the shaft output (kinetic energy) of the internal combustion engine is recovered by the power output shaft electric power generator and converted into electric energy. This converted electric energy is supplied to the electricity storing means, or otherwise satisfies an electric load in the vehicle. In other words, since the energy amount contained in exhaust gas is excessively reduced during deceleration of the vehicle, recovery of energy cannot be sufficiently accomplished under electric power generation only with the exhaust gas electric power generator. However, the present invention provides for recovery as electric energy the vehicle kinetic energy which has been hitherto released as engine brake or frictional heat due to operation of a brake pedal.
According to the certain embodiments of the invention, when there arises, for example, an abnormality or a deterioration in the exhaust gas electric power generator, electric power generation can be accomplished by operating the power output shaft electric power generator as a main electric power generating source. This can stably supply an electric power required for the vehicle, thereby improving the reliability of the electric energy supply system.
The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.